Electron-emitting cathode and process of preparing the same



1,639,698 Aug. 23, 1927. F. HOLBORN I ELECTRON EMITTING CATHODE AND PROCESS OF PREPARING THE SAME Filed Jan. 14, 1926 INVENTOR fieder/kk ho/am Y Ehvwu, I ay/w, mamVM ATTORN EY5 Patented Aug. 23, 1927.

UNITED STATES PATENT OFFICE.

FREDERICK HOLBOBN, OF HOBOKEN, NEW JERSEY, ASSIGNOR TO HAZELTINE COR- PORATION, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF DELAWARE.

l ELECTRON-EMITTING GATHODE AND PROCESS PREPARING THE SAME.

Application filed January 14, 1928. Serial No. 81,163.

In the manufacture of oxide coated electron-emitting cathodes much diflicnlty has been encountered due to the fact that it has been impossible to obtain coatings of the 5 pure oxide of the alkali-earth since these materials have a tendency to absorb carbon dioxide and water which tend to change the oxides into hydroxides and carbonates.

- In accordance with the resent invention,

an improved process of o taining substantially pure oxides on the filament is provided by making a colloidal solution of the alkaliearth' metal employed and then changing this material to an oxide without using the 1 intermediate steps of reducing the oxide from a carbonate or hydrate of the metal.

The method employed will best be under-- stood by describing the various steps followed in'the manufacture of an electronemitting cathode. A colloidal solution ofone or more of the alkali-earth metals, such as calcium, barium or strontium, is produced by sputtering electrodes of these materials under pyridine (C H N) which is effected in the following manner:

A vessel, such as 5, containing pyridine, has electrodes 6 and 7 immersed therein. These electrodes may be formed of some alkali-earth metal, such as calcium, strontium or barium, or one of these electrodes may be of strontium and the other of barium, or any combination of these metals. It is also possible to use misch-m'etal for the several electrodes. These electrodes form a sparkap and. are electrically connected throng condensers 8 to the secondary winding 9 of a transformer, the primary winding 10 of which is connected to high frequency oscillators 11 preferably of the vacuum tube type, generall designated 12. This transmitter has inclu ed in its circuit small inductance and large capacity for the purpose of developing a low volta e and large current of hi h frequency. Un er the action of a high equency are thus developed the metal of the electrodes 6 and 7 is sputtered in the form of fine articles into the pyridine to form a colloi a1 solution. The particular advantage of the use of pyridine is that the calcium, barium or strontium, does not form oxides until all the pyridine has been evaporated. High fre qnency is used to prevent any electrolytic effects.

The colloidal solution thus prepared may be applied in any suitable manner, such as by dipping, or by an electrophoresis method,

which consists in placing the filament in the oteneach weighing about two grams, were immersed in a vessel containing fifty cubic centimeters of pyridine. between the electrodes and a current was passed between them through the pyridine for about one-half hour until a homogeneous colloidal solution, dark brown in color, was formed. For this current, a high frequency vacuum tube oscillator having an-output of fifty watts at a frequency of one and onehalf million cycles was used. The colloidal solution thus formed was permitted to stand about a day to permit the arger particles to settle. The colloidal solution of metallic calcium thus obtained was then applied by electrophoresis to a platinum filament about ten m1ls wide and one-half mil thick, by placing the filament in the colloidal solution in which there was suspended a platinum electrode about one-half inch wide and onehalf mil thick and adifierenc'e of potential of ten volts was developed between the filament and the electrode with the filament being maintained negative. The filament was left in the solution for about one-half hour at which time a black coating was present on the filament. The filament wasthen heated in air at about 150C. to evaporate the py- An arc was developed ridine and, it was then further heated in air for about ten minutes at 700 C. to change the calcium to an oxide. The coating obtained in this manner was very fine and adhered strongly to the filament I claim: i

1. The process of preparing an electronemitting cathode which consists in suspending finely divided metal of the alkali-earth groupin a non-oxidizing medium, electrically depositing the metal from said medium on a conductor, and subjectng said conductor to heat.

2. The 'process of preparing an electronemitting cathode which consists in forming a colloid solution of an alkali-earth metal by sputtering said metal in a liquid by means of a high frequency are, depositing said colloidal metal on a conductor to form a coating, and then-heating the coated conductor.

3. The process of preparing an electronemitting cathode which consists in suspending a finely divided metal of the alkali-earth group in pyridine, applying a coat of metal in pyridine to a conductor, and subjecting the conductor to heat to evaporate the pyridine.

4. The process of preparing an electronemitting cathode WhlCh consists in sputtering a metal of the alkali-earth group in I pyridine, applying the metal in pyridine to a conductor, and subjecting the conductor to heat to evaporate the pyridine.

5. The process of preparing an electronemitting cathode which consists in sputtering? a metal of the alkali-earth group in pyridine, electrically depositing the sputtered metal from the pyridine on a conductor, and subjecting the conductor to heat to evaporate the pyridine.

6. The process of preparing an electronemitting cathode which conslsts in sputtering a plurality of metals of the alkaliearth group in pyridine, applying the metals suspended in the pyridine to a conductor, and then subjecting said conductor to heat to evaporate the pyridine.

, In testimony whereof I aflix my signature.

FREDERICK HOLBORN. 

